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doc: improve description of system time in tracking report

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Miroslav Lichvar 2022-08-29 12:07:10 +02:00
parent 166e43b13e
commit a07ac38331
1 changed files with 13 additions and 9 deletions
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doc/chronyc.adoc
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@ -180,15 +180,19 @@ stratum-2 and is synchronised from a stratum-1).
This is the time (UTC) at which the last measurement from the reference This is the time (UTC) at which the last measurement from the reference
source was processed. source was processed.
*System time*::: *System time*:::
In normal operation, *chronyd* by default never steps the system clock, because This is the current offset between the NTP clock and system clock. The NTP
any jump in the time can have adverse consequences for certain application clock is a software (virtual) clock maintained by *chronyd*, which is
programs. Instead, any error in the system clock is corrected by slightly synchronised to the configured time sources and provides time to NTP clients.
speeding up or slowing down the system clock until the error has been removed, The system clock is synchronised to the NTP clock. To avoid steps in the
and then returning to the system clock's normal speed. A consequence of this is system time, which might have adverse consequences for certain applications,
that there will be a period when the system clock (as read by other programs) the system clock is normally corrected only by speeding up or slowing down (up
will be different from *chronyd*'s estimate of the current true time (which it to the rate configured by the <<chrony.conf.adoc#maxslewrate,*maxslewrate*>>
reports to NTP clients when it is operating as a server). The value reported directive). If the offset is too large, this correction will take a very long
on this line is the difference due to this effect. time. A step can be forced by the <<makestep,*makestep*>> command, or the
<<chrony.conf.adoc#makestep,*makestep*>> directive in the configuration file.
+
Note that all other offsets reported by *chronyc* and most offsets in the log
files are relative to the NTP clock, not the system clock.
*Last offset*::: *Last offset*:::
This is the estimated local offset on the last clock update. A positive value This is the estimated local offset on the last clock update. A positive value
indicates the local time (as previously estimated true time) was ahead of the indicates the local time (as previously estimated true time) was ahead of the